Memory devices provide data storage for electronic systems. One type of memory is a non-volatile memory known as flash memory. A flash memory is a type of EEPROM (electrically-erasable programmable read-only memory) that may be erased and reprogrammed in blocks. Many modem personal computers have BIOS stored on a flash memory chip. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in wireless electronic devices because it enables the manufacturer to support new communication protocols as they become standardized, and to provide the ability to remotely upgrade the devices for enhanced features.
A typical flash memory comprises a memory array that includes a large number of memory cells arranged in row and column fashion. The cells are usually grouped into blocks. Each of the cells within a block may be electrically programmed by charging a charge-storage material. The charge may be removed from the charge-storage material by a block erase operation. Data is stored in a cell as charge in the charge-storage material.
NAND is a basic architecture of flash memory. A NAND cell unit comprises at least one selecting device coupled in series to a serial combination of memory cells (with the serial combination being commonly referred to as a NAND string).
A continuing goal of semiconductor fabrication is to increase integration. Accordingly, it is desired to develop new NAND architecture which consumes less semiconductor real estate than conventional NAND architecture, and to develop methods of forming such new NAND architecture.